High penetration deposition process and apparatus

ABSTRACT

A method and apparatus for deep penetration deposition of material in a porous substrate utilizes a pressure differential across the substrate to effect penetration of arc-produced vapor from one chamber through the body. The one chamber can be held at a pressure of 10 -2  to 10 -3  torr while the other chamber is at a pressure of 10 -5  to 10 -6  torr.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of co-pending application 07/276,068 filed on 25Nov., 1988.

This application is related to my copending application Ser. No.06/941,185 filed 12 December 1986 and to subject matter disclosed inearlier applications linked to this copending application and havematured into U.S. Pat. Nos.: 4,351,855, 4,438,153, 4,505,948, 4,537,794,4,548,670 4,565,711 4,569,307 4,575,401.

In addition, reference may be had to my copending application Ser. No.07/208,886 filed 17 June 1988.

FIELD OF THE INVENTION

My present invention relates to a method of and an apparatus foreffecting deposition of a material into interstices of a fully orpartially porous body, to the production of a high-density structureutilizing such deposition of material, to apparatus for carrying out themethod and to a method of and an apparatus for effecting the plugging ofcracks, fissures or pores in a pipe or similar element.

BACKGROUND OF THE INVENTION

The aforementioned copending applications and patents are concerned withlow-temperature deposition processes, and apparatus for carrying out theprocesses, whereby the deposited material can be derived by striking anarc between electrodes in an evacuated space at relatively high currentsand low voltages to vaporize a substance from one of these electrodes.

That substance may, in turn, be deposited upon a surface or thatsubstance may react with other elements or substances present in theremaining atmosphere within the evacuated chamber, or with substancesfrom the other electrode or from other electrodes to produce compounds,such as ceramics, which can be deposited upon substrates.

Frequently, however, it is desirable to obtain penetration of depositedmaterials significantly into the depth of a porous body or, in anappropriate case, to fill the pores or interstices of a body with adeposited material.

A specific case in which depositing a material in deep intersticialspaces is of advantage, is the plugging of a pipe in which theinterstices may be cracks, macropores, microporous structures or thelike.

Naturally, even prior to the arc vapor deposition techniques disclosedin the earlier applications and patents, there were attempts to depositmaterials of a considerable depth within a substrate. For example,attempts have been made to utilize chemical vapor deposition orelectroless or chemical plating techniques for this purpose and even touse electrodeposition techniques.

By and large these techniques have failed partly because deposits formrapidly on the regions closest to the source of the deposited materialand prevent further penetration of the material. Most earliertechniques, moreover, are incapable of substantially completely fillingthe pores of porous bodies or structures and have not proved to besatisfactory for that reason.

OBJECTS OF THE INVENTION

The principal object of the present invention is to provide adeep-penetration deposition method whereby materials can be deposited torelatively great depths in a porous structure without the drawbacks ofearlier systems, even to the point that high-density articles can befabricated.

It is another object of this invention to provide an improved method ofmaking high-density materials utilizing a deposition approach.

Yet another object of this invention is to provide a method of sealingcracks, pores or interstices in a pipe.

It is also an object of the present invention to provide an improvedmethod of making metal matrix materials.

Still another object of my invention is to provide an improved apparatusfor carrying out the methods of the invention.

SUMMARY OF THE INVENTION

These objects and others which will become apparent hereinafter areattained, in accordance with the present invention by a method whichinvolves the application of a force gradient across a porous bodybetween a subatmospheric first chamber and a subatmospheric secondchamber, thereby inducing penetration of material formed in the firstchamber through the body toward the second chamber, the material in thefirst chamber being generated preferably by arc vapor deposition.

More particularly, I can produce a high-density structure in a productby providing a porous body and disposing it between two chambers whileevacuating the first chamber to a reduced pressure sufficient to enablean arc discharge to be created to generate vapor of a substance to bedeposited as part of the material which is driven into the body by thepressure differential applied thereacross.

The method of the invention for producing a high-density structure canthus comprise the steps of:

(a) disposing a body of a porous material between two chambers;

(b) evacuating one of the chambers to a subatmospheric pressure adaptedto sustain vapor formation by an electrical discharge;

(c) effecting an electrical discharge in the one of the chambers tovaporize a substance therein; and

(d) evacuating the other of t he chambers to a lower subatmosphericpressure and a higher vacuum than that in the one of the chambers andthereby inducing the substance to penetrate into the body and deposit ininterstices thereof in the form of a deposited material.

The substance can be vaporized from an electrode in the one or firstchamber by striking an arc between these electrodes and acounterelectrode, e.g. by moving the electrodes into contact and apartas described in the aforementioned copending applications and patents,while a voltage of, for example 20 to 150 volts, is applied across theelectrodes so that the arc, when it is struck, will have an arc currentof 40 to 150 amperes.

According to a feature of the invention, a pressure of about 10⁻² to10⁻³ torr is maintained in the first chamber while the pressure in thesecond chamber is maintained at 10⁻⁵ to 10⁻⁶ torr.

Surprisingly, under these conditions the material vaporized in the firstchamber appears to be deposited in the porous body to practicallycompletely fill the pores thereof so that especially high-densityproducts can be made.

The porous body can be a metal matrix, which can be formed by metalfilaments or fibers forming a nonwoven fabric. Preferably, however, Iprefer to fill the interstices of a body of the type made by the methoddescribed in my copending application Ser. No. 07/208,886 before orafter compaction of this material. That material can be formed in turnby utilizing the arc vapor deposition method of the invention to coatthe walls of the open pore or reticulate structure of a synthetic resinfoam whereupon the coated product can be pyrolyzed to leave an openworkwhich can be filled by application of a pressure differential across thebody in the manner described.

It is possible, in accordance with the invention, to form the firstchamber within the interior of a pipe which can constitute the bodywhose pores are to be filled. The pipe, in turn, can be surrounded by anenclosure defining the second chamber downwardly of the pipe wall andwith other means closing the ends of the pipe. The first chamber is thendefined within the interior of the pipe.

In practice, this approach can be used for the deposition of materials,including ceramics, within interstices discovered in a pipe wall so asto plug those interstices.

Other porous bodies or substrates can be used with equal advantage. Forexample, if one wishes, the porous body can be constituted as a fabricor nonwoven fiber structure. Alternatively, the body can be a syntheticresin foam which is not destroyed. It can also be constituted as acloth.

According to a feature of the invention, an apparatus for carrying outthe process can comprise:

means defining two chambers on opposite sides of the body;

means for evacuating one of the chambers to a subatmospheric pressureadapted to sustain vapor formation by an electrical discharge;

means for effecting an electrical discharge in the one of the chambersto vaporize a substance therein; and

means for evacuating the other of the chambers to a lower subatmosphericpressure and a higher vacuum than that in the one of the chambers andthereby inducing the substance to penetrate into the body and deposit ininterstices thereof in the form of a deposited material.

The material which is deposited can be a metal identical with a metalvaporized from one of the electrodes. Alternatively, the substance whichis vaporized from the electrode can be a compound or alloy correspondingto the composition of the electrode.

In another system within the present invention, the deposited materialis formed in situ within the first chamber by reaction of a componentadmitted to the chamber with the substance vaporized from the electrode.

The apparatus can have parts flanged together to position the workpiecebetween the two chambers and for a flange connection of respective pumpsto the chambers for evacuating them to the desired levels.

An electrode rod can extend through the pipe which is to be plugged, inaccordance with the invention, so that wide-area coating techniques asdescribed in my earlier patents can be applied in a convenient manner.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the presentinvention will become more readily apparent from the followingdescription, reference being made to the accompanying drawing in which:

FIG. 1 is a side elevational view, partly in cross section, of anapparatus for carrying out the method of the present invention in thefilling of a porous body; and

FIG. 2 is a similar section of an apparatus for plugging holes in a pipeby the method of the invention.

SPECIFIC DESCRIPTION

In FIG. 1 I have shown a chamber 10 which can evacuated to asubatmospheric pressure of 10⁻² to 10⁻³ torr by a vacuum pump 11connected by a flange coupling 12 to the vacuum chamber 10. Within thevacuum chamber I provide a support 13 for a pair of electrodes 14 atleast one of which is composed of a substance which is to be present inmaterial to be deposited.

The electrodes can be reciprocated as described in my earlierapplications and patents by a mechanism 15 or 16 so that an arc can bestruck between the electrodes to vaporize the substance in a space 17under the pressure maintained within chamber 10. A voltage source 18 isconnected across the electrodes so that the arc is struck at a potentialof 20 to 150 volts and can have an arc discharge current of say 40 to150 amperes.

The chamber 10 can communicate with a nitrogen source 19 representing asource of any gaseous component which can chemically combine with thevaporizable substance to permit the deposition of a compound or alloy inthe porous body 20 to be penetrated by the deposited material.

The porous body 20, which can be a metal matrix, a nonwoven fiber massof metal or synthetic resin or even natural-fiber filaments, a cloth padsintered metal body or even a plated glass structure, can be held in aholder 21 connected to the space 17 by a flange coupling 22 and by acoupling 23 to a pipe 24 communicating via a further pipe 25 with avacuum pump 26 adapted to generate a subatmospheric pressure of say 10⁻⁵to 10⁻⁶ torr.

The space 17 on one side of the porous body 20 is thus at asubatmospheric pressure which is low enough to sustain an effective arcdischarge to produce a vapor of a substance of one of the electrodes butwhich is higher than the pressure in a chamber 27 at the opposite sideof the porous body.

The vapor when it is formed and any compound which it may form asdescribed, has been found to penetrate the body under a force gradientwhich results from the pressure differential across the body and,surprisingly, results in a filling of the interstices with the materialwhich is thus deposited.

For example, I may fabricate a metal matrix utilizing the principlesdescribed in my application Ser. No. 07/208,886, e.g. of nickel, andthen fill the interstices thereof utilizing the apparatus of FIG. 1with, for example, titanium nitride by utilizing titanium for theelectrodes and admitting nitrogen to the chamber 10 and the space 17. Aceramic-filled nickel metal matrix thus can result.

When one of the electrodes is composed of tungsten or silicon, forexample, the other electrode can be composed of carbon so that siliconcarbide can form and deposit in the metal matrix.

Instead of a metal matrix, of course, I may use a foam, e.g. of the typeused to make the metal matrix in Ser. No. 07/208,886 and substantiallyfill the interstices thereof with the metal or metal alloy or a metalcompound.

SPECIFIC EXAMPLE

A nickel openwork structure adapted to constitute a metal matrix is madeby subjecting an 80-pores-per-inch open-pore flexible reticulated ester,polyurethane foam of a density of about 1.75 pounds per cubic foot and athickness of approximately 1/16th of an inch to low temperature arcvapor deposition in a vacuum chamber to which a vacuum of 10⁻⁵ torr hasbeen applied using nickel electrodes between which the arc is struck.The applied voltage is 40 volts and an arc current of about 75 amperesis drawn. The process is carried out until the substrate is coated tothe full thickness thereof.

The metal-coated polyurthane foam, coated with approximately 50 grams ofnickel per square foot is subjected to pyrolysis in the presence of airin an electric furnace for 2 minutes at 350°C. to completely eliminatethe polyurethane structure. The substrate is then subjected to sinteringin a vacuum furnace at 950°C. to 1250°C., preferably about 1100°C. for aperiod of 5 to 60 minutes, preferably about 15 minutes. The nickelstructure has up to 95% porosity.

A stack of substrates as thus made, forming a body with a totalthickness of one inch, is impregnated with titanium nitride by the useof the apparatus of FIG. 1. In that apparatus, the electrodes arecomposed of titanium and the arc discharge is effected by striking anarc between the electrodes. The voltage across the electrodes is about50 volts and the arc current is about 75 amperes. A vacuum of 10⁻³ torris maintained in chamber 17 and a vacuum of 10⁻⁵ torr is maintained inchamber 27.

Nitrogen is admitted to the chamber 17 and titanium nitride is depositedin the interstices in the stack of substrate under the pressuredifferential thereacross. Upon weighing the porous body after 20 to 30minutes, it is found that the pores of the porous body have beenpractically completely filled with titanium nitride, imparting a densestructure to the body.

In FIG. 2 I have shown how the principles of the invention can beapplied to the plugging of pores in a porous pipe 30. The pores in thispipe can be intentionally left therein if it is desired to have thepores filled with a ceramic material such as chromium nitride ortitanium nitride. The pores may also be a result of cracks generated inthe formation of the pipe or in the use thereof. The cracks can befilled with chromium, titanium, nickel or alloys thereof or ceramics.

The pipe 30 is mounted between plates 31 and 32 to which the pipe isflanged and which support, in addition, an outer cylindrical member 33defining an outer chamber 34 to which flange connection 35 can connect avacuum pump 36 adapted to generate a suction of 10⁻⁵ to 10⁻⁶ torr in thechamber 34.

Another vacuum pump 36 is connected by a pipe 37 and correspondingflange connections to the chamber 38 formed on the interior of the pipe30.

An electrode 39 is mounted in the pipe 37 and by a spider 40 on theplate 31 so as to extend centrally within the pipe 30.

A counter electrode 41 is mounted on the plate 32 and can be movedtoward and away from the electrode 39 to strike an arc therewith. Themechanism 42 for displacing the electrode 41 to strike the arc ismounted on the plate 32. The voltage source 43 is connected across theelectrodes.

Essentially, the apparatus shown in FIG. 2 operates in accordance withthe same principles as the apparatus of FIG. 1. A driving force iscreated across the wall of the pipe 30 by the pressure differentialbetween the chambers 38 and 34 because of the differential evacuation ofthese chambers by the respective pumps. When an arc is struck, thedischarge travels along the electrode 39 vaporizing material therefrom,e.g. nickel or chromium, to permit this material to penetrate throughinterstices or pores, holes or micropores in the pipe wall. Thepenetration of the deposited material is to the full thickness of thepipe wall and the deposited material can plug the cracks or pores in thelatter.

I claim:
 1. An apparatus for effecting filling of interstices of a bodywith a deposited material, comprising:means defining two chambers onopposite sides of said body; means for evacuating one of said chambersto a subatmospheric pressure adapted to sustain vapor formation by anelectrical discharge; means for effecting an electrical discharge insaid one of said chambers to vaporize a substance therein; and means forevacuating the other of said chambers to a lower subatmospheric pressureand a higher vacuum than that in said one of said chambers and therebyinducing said substance to penetrate into said body and deposit ininterstices thereof in the form of a deposited material.
 2. Theapparatus defined in claim 1 wherein said means for effecting anelectrical discharge in said one of said chambers includes means forstriking an electric arc between an electrode composed of said materialand a counterelectrode.
 3. The apparatus defined in claim 2 wherein saidcounterelectrode is composed of a material reacting with said substanceto form a ceramic as said deposited material.
 4. The apparatus definedin claim 2 wherein said one of said chambers is provided with means foradmitting a gas thereto for reaction with said substance to form aceramic as said deposited material.
 5. The apparatus defined in claim 2wherein said means for evacuating one of said chambers is a vacuum pumpadapted to generate a vacuum of 10⁻² to 10⁻³ torr in said one of saidchambers and said means for evacuating the other of said chambers is avacuum pump adapted to generate a vacuum of 10⁻⁵ to 10⁻⁶ torr in saidother of said chambers.
 6. The apparatus defined in claim 2 wherein saidbody is a pipe, said one of said chambers is formed within said pipe andsaid other chamber surrounds said pipe, said electrode extendinglongitudinally within said pipe.